This invention relates generally to machine tools and more particularly, this invention relates to a motorized nut for use in combination with a lead screw for precisely displacing a movable machine tool member on a fixed machine tool member along a straight path.
In the design of various types of machinery, and particularly machine tools, an important design criterion is the ability to precisely displace a movable member, such as an axis slide in the case of a machine tool, on a fixed member, such as the machine tool bed, along a straight path. Invariably, where precise movable member positioning is required, the combination of a lead screw, and a nut, and in particular, a ball type lead screw, and ball nut have been employed, the ball nut typically being secured to the movable member while the ball screw is rotatably journaled in the fixed member in threaded cooperation with the ball nut for displacing the movable member along the fixed member responsive to ball screw rotation.
In present day machine tools which employ the combination of a ball screw and a ball nut for precisely displacing a machine tool axis slide on the machine tool bed, the ball screw is typically driven from either an electric or a hydraulic motor through a gear box. Driving the ball screw from the motor through a gear box yields superior machine tool performance in contrast to directly driving the screw from the motor via universal coupling as the direct drive arrangement suffers from greater backlash due to the resiliency of the universal coupling. Further, use of a gear box to couple the motor to the ball screw affords greater rigidity to the ball screw which is very desirable. The disadvantage of employing a gear box to couple the ball screw to the motor is that such gear boxes are costly to manufacture. Further, while employing a gear box to couple the motor to the ball screw reduces backlash as compared to coupling the motor directly to the ball screw via a universal coupling, still some backlash is inherent with the gear box which reduces positioning accuracy.
In comparison, the present invention concerns a positioning system employing a motorized nut in combination with a rigid lead screw and this, eliminates the above-enumerated disadvantages of the prior art lead screw nut positioning mechanisms.
It is an object of the present invention to provide a positioning system employing a motorized nut in combination with a rigid lead screw so as to achieve minimum backlash between the screw and the nut.
It is yet another object of the present invention to provide a positioning mechanism including a motorized nut and a rigidly fixed lead screw to assure rigid coupling between the movable member and the fixed member as the movable member is displaced thereacross.